A recent trend in wavelength division multiplexed (WDM) optical fiber systems and networks is to increase the per wavelength data rate to 40 Gb/s or higher. However, increasing data rate limits the maximum achievable distance because of degradation of signals caused by two fundamental physical phenomena i.e., fiber dispersion and fiber nonlinearity. In high speed WDM systems, interaction of fiber nonlinearity and dispersion manifests in many degrading effects limiting the total capacity as well as the achievable transmission distance. Fiber nonlinearity is a fundamental degrading effect in high speed WDM systems. With per channel data rate approaching to 40 Gb/s or higher in WDM systems, the degrading effects caused by fiber nonlinearity become mainly single channel effects e.g., self-phase modulation (SPM), intra-channel cross-phase modulation (IXPM), and intra-channel four-wave mixing (IFWM).
Many optical techniques to mitigate the effect of fiber nonlinearity have been proposed, though substantially most of the optical techniques do not compensate fiber nonlinearity but tend to mitigate or manage the effect of nonlinearity to begin with. The only exception is optical conjugation technique which tends to directly compensate optical nonlinearity by optical conjugation of the optical signal in the middle of the link and propagating the conjugated signal through the remaining half of the link which needs to be symmetric to the first half. In addition to optical techniques, many electronic techniques e.g., forward error correction (FEC) and digital signal processing (DSP) have been proposed for mitigating the dispersive and nonlinear degrading effects in WDM transmission systems. FEC technique inherently improves the transmission system performance by allowing the system to work at low signal-to-noise-ratio (SNR) and thereby mitigating the fiber nonlinearity. On the contrary, other DSP techniques tend to directly compensate the degradation caused by fiber dispersion and nonlinearity. Some of the recent DSP techniques have shown successful compensation (both pre and post compensation) of fiber dispersion alone, while some other techniques have shown successful pre-compensation of fiber nonlinearity. However, none of these techniques has successfully demonstrated the post-compensation of degrading effects already caused by fiber nonlinearity in spite of some attempts for simultaneous post compensation of fiber dispersion and nonlinearity.
The following publications provide additional information:    [1] R. J. Essiambre, B. Mikkelsen, and G. Raybon, “Intrachannel cross phase modulation and four wave mixing in high speed TDM systems”, Electron. Lett., vol. 35, no. 18, pp. 1576-1578, 1999.    [2] R. I. Killey, H. J. Thiele, V. Mikhailov, and P. Bayvel, “Reduction of intrachannel nonlinear distortion in 40-Gb/s-based WDM transmission over standard fiber”, IEEE Photon. Technol. Lett., vol. 12, pp. 1624-1626, 2000.    [3] H. Bulow, F. Buchali, and A. Klekamp, “Electronic Dispersion Compensation”, IEEE/OSA JLT, vol. 26, pp. 158-167, January 2008.    [4] Jin Wang and Joseph M. Kahn, “Performance of electrical equalizers in optically amplified OOK and DPSK systems”, IEEE Photon. Technol. Lett., vol. 16, pp. 1397-1399, May 2004.    [5] V. Curri, R. Gaudino, A. Napoli and P. Poggiolini, “Electronic equalization for advanced modulation formats in dispersion-limited systems”, IEEE Photon. Technol. Lett., vol. 16, pp. 2556-2558, November 2004.    [6] Kim Roberts, Chuandong Li, L. Strawczynski, M. O'Sullivan, and I. Hardcastle, “Electronic Precompensation of Optical Nonlinieairity”, IEEE Photon. Technol. Lett., vol. 18, pp. 403-405, January 2006.    [7] Neal S. Bergano, “Undersea communications systems”, in Optical Fiber Telecommunication IVB Systems and Impairments, Ivan Kaminow and Tingye Li, Eds. San Diego, Calif.: Academic Press 2002, pp 154-197.    [8] A. H. Gnauck, “Advanced amplitude and pulsed coded formats for 40-Gb/s Fiber Transmission” in IEEE's 17th Annual Meeting of LEOS Technical Digest, 2004, vol. 2, pages 605-606.    All publications listed above are incorporated by reference in their entirety herein, as though individually incorporated by reference.